1. Field of the Invention
This invention relates generally to measuring systems for measuring position of movable machine members. In particular, this invention relates to interconnection between position measuring devices and an interface circuit.
2. Description of the Prior Art
It is known to use two position measuring devices to measure absolute position of a movable machine member. For example, by providing slightly different reductions in the drive to the rotors of two angular position measuring devices, a difference between the position measured by each device is generated which will assume a unique value throughout the range of motion of the machine member. This difference provides a value which may be conveniently used to determine the absolute position of the machine member, even though neither measuring device is suitable for independently indicating the machine member absolute position throughout the full range of motion.
Further, it is known to use resolvers as the position measuring devices in absolute position measuring systems employing angular position measuring devices. Each resolver provides inductive coupling of input signals between rotor and stator elements such that the phase of resolver output signals relative to the input signals is a function of the rotor mechanical location relative to the stator. By driving the rotors of two resolvers differentially relative to one another, the angular position of each rotor detected by a conventional interface will provide the desired difference for determining absolute position. Techniques for use of revolvers in this fashion are described in U.S. Pat. No. 4,580,209.
It will be appreciated that the use of two angular position measuring devices has the inherent disadvantage of increasing the number of conductors required between an interface circuit and the machine where the measuring devices are mounted.